People are trapped by floodwaters and facing dwindling supplies of medicines, food and drinking water. Carbon monoxide poisoning is a danger as people crank up portable generators, and respiratory viruses will circulate in crammed shelters.

On Monday morning, in Maxton, N.C., Dan Lowry, 48, and his wife, Jewel, 51, trudged through the waist-high water around Dan’s father’s house, aware of the dangers around them."